The continued development, study, and bioanalytical applications of newly devised potentiometric gas sensing systems are proposed. These systems will be prepared by using various polymer membrane ion-selective electrodes as internal sensing elements in static and automated gas sensing arrangements. One priority will be the fabrication of inexpensive carbon dioxide and ammonia sensing catheters which may ultimately be useful for continuous in-vivo monitoring of these gases. Such devices will be constructed by utilizing miniature internal silver-silver chloride reference electrodes coated with appropriate polymeric materials. Attempts will also be made to utilize these miniature sensors in conjunction with immobilized enzymes to prepare simple yet durable probes for the continuous detection of metabolites, amino acids and similar biomolecules. Furthermore, through the systematic investigation of various organic anion complexing molecules, expanded efforts will be made to prepare a bicarbonate responsive polymer membrane which will be used to develop a CO2 sensor with improved response properties. In addition, new static gas sensors will be developed for the measurements of nitrogen oxides, hydrogen sulfide and hydrogen cyanide. Such sensors will be prepared by using internal nitrate, sulfide and cyanide responsive polymer membrane electrodes and appropriate inner buffer reagents. Automated instruments capable of continuously monitoring these gases will also be constructed through the use of tubular forms of the polymer electrodes and a continuous flow gas dialysis approach. Finally, the new gas sensing systems proposed and the ones already developed in the first phase of this project will be applied as detectors in several novel bioanalytical investigations, including: the development of a highly selective creatinine analyzer, and the continued development of toxicity biomonitors based on enzyme and living cell reagents.